The present invention relates to a dust collecting filter which is used for filtering a fluid containing particles (hereinafter will be called "dust").
Conventionally, the filter of this type has been formed of a plate shaped or block shaped porous filter member provided with interconnected pores, or formed by folding a band shaped filter member similar to accordion pleats.
In order to collect dust of which the particle diameter is comparatively large, a plate or block shaped filter member having large pores or meshes and comparatively small flowing resistance has been used, and in order to collect dust of which the particle diameter is comparatively small, a folded filter member having small pores or meshes and comparatively large flowing resistance has been used.
These conventional filters have been mainly used for filtering a fluid containing dust of which the density is low and of which the particle diameter is nearly constant. However, these conventional filters are not suitable for filtering a fluid containing dust of which the density is high and of which the particle diameter is widely distributed, i.e. varies considerably.
Thus, when a conventional filter having large meshes as described above is used, a considerable amount of dust passes the filter without being collected thereby so that high dust collecting efficiency cannot be obtained. When a conventional filter having small meshes as described above is used, the filter is apt to be clogged by the dust so that the pressure loss is increased in the filter.
Accordingly, one object of the present invention is to provide a dust collecting filter, the whole of which can be effectively used for filtering the fluid without being partially clogged by the dust and which has improved dust collecting efficiency.
Another object of the present invention is to provide a small size light weight filter which can filter a fluid containing dust of which the particle diameter is widely distributed, over a long period of time with high collecting efficiency.